This is a multi-center, prospective randomized clinical study to evaluate the clinical outcome of subjects with DDD who are treated with ALIF and supplemental posterior fixation using Aspen compared to pedicle screw instrumentation. The study will involve up to approximately 25 investigational sites and enroll up to 156 67 subjects. The randomization ratio of two Aspen subjects to one pedicle screw subject (2:1) will be utilized.